"Our purpose was to introduce people to the world of Columbia, to Elizabeth and to Booker DeWitt. Yeah, there are some demo-ey things in there that help progress the action."

BioShock Infinite, due out in 2012, is set in a flying city called Columbia. You play Booker DeWitt, a former Pinkerton agent who's trying to track down a woman trapped aboard the crumbling dystopia.

"When we're looking at what BioShock Infinite will ship as, it'll be much more, as far as pacing goes, like BioShock 1," Robertson added.

"It's very important to us that the player has time to explore. For those who enjoy being the environment, they can explore and take as long as they want. For those who just want to blow through it and get the story done, well they can avoid all the exploration areas and just plough through the story as quick as they can.

"It will be a game that'll definitely have a couple of set pieces, but it's not going to be watching a movie and going from big moment to big moment to big moment."